Modern traffic management systems use broadcast methods with limited geographic targeting to provide environmental information and conditions. The information is also reactive versus proactive for those receiving said information. The most defined areas around an incident are usually based on traffic management center nodes and/or other location determinations (location referencing objects (LRO), dynamic location referencing (DLR), location referencing methods (LRMs)) which are then broadcast as generic incident information which is then used to communicate information that can be translated into new destination arrival times or generic alerts. Two main types of messaging are used in current communication systems: Cooperative Awareness Messages (CAM) and Decentralized Event Notification Messages (DENM).
Cooperative Awareness Messages (CAM) are the message communication pattern in which every vehicle in the network sends a message to every other vehicle within its range of communication periodically. These messages generally include the geographical location of the vehicle, the velocity of the vehicle, and the basic status of communicating vehicles to neighboring vehicles that are located within a single hop distance.
Decentralized Event Notification Messages (DENM) are generated when a certain hazardous event (e.g. accident) has taken place on the road. The generation of these messages is dependent on the occurrence of certain events. Such an event is not routinely transmitted as CAMs. DENMs are also termed as event triggered messages and the messages do not have any fixed schedule of transmission. The value of information of DENMs is much more than that of CAMs since it is directly related to the road safety applications.